File: README — Documentation for arturo (2.0.0)

What

Arturo provides feature sliders for Rails. It lets you turn features on and off just like feature flippers, but offers more fine-grained control. It supports deploying features only for a given percent* of your users and whitelisting and blacklisting users based on any criteria you can express in Ruby.

* The selection isn't random. It's not even pseudo-random. It's completely
  deterministic. This assures that if a user has a feature on Monday, the
  user will still have it on Tuesday (unless, of course, you *decrease*
  the feature's deployment percentage or change its white- or blacklist
  settings).

A quick example

Trish, a developer is working on a new feature: a live feed of recent postings in the user's city that shows up in the user's sidebar. First, she uses Arturo's view helpers to control who sees the sidebar widget:

<%# in app/views/layout/_sidebar.html.erb: %>
<% if_feature_enabled(:live_postings) do %>
<div class='widget'>
  <h3>Recent Postings</h3>
  <ol id='live_postings'>
  </ol>
</div>
<% end %>

Then Trish writes some Javascript that will poll the server for recent postings and put them in the sidebar widget:

// in public/javascript/live_postings.js:
$(function() {
  var livePostingsList = $('#live_postings');
  if (livePostingsList.length > 0) {
    var updatePostingsList = function() {
      livePostingsList.load('/listings/recent');
      setTimeout(updatePostingsList, 30);
    }
    updatePostingsList();
  }
});

Trish uses Arturo's Controller filters to control who has access to the feature:

# in app/controllers/postings_controller:
class PostingsController < ApplicationController
  require_feature :live_postings, :only => :recent
  # ...
end

Trish then deploys this code to production. Nobody will see the feature yet, since it's not on for anyone. (In fact, the feature doesn't yet exist in the database, which is the same as being deployed to 0% of users.) A week later, when the company is ready to start deploying the feature to a few people, the product manager, Vijay, signs in to their site and navigates to /features, adds a new feature called "live_postings" and sets its deployment percentage to 3%. After a few days, the operations team decides that the increase in traffic is not going to overwhelm their servers, and Vijay can bump the deployment percentage up to 50%. A few more days go by and they clean up the last few bugs they found with the "live_postings" feature and deploy it to all users.

Installation

In Rails 3 or 4, with Bundler

gem 'arturo', '~> 1.0'

In Rails 3 or 4, without Bundler

$ gem install arturo --version="~> 1.0"

In Rails 2.3

Rails 2.3 is no longer supported and has been archived on the rails_2_3 branch.

Configuration

In Rails

Run the generators:

$ rails g arturo:migration
$ rails g arturo:initializer
$ rails g arturo:routes
$ rails g arturo:assets

Run the migration:

$ rake db:migrate

Edit the generated migration as necessary

Edit the configuration

Initializer

Open up the newly-generated config/initializers/arturo_initializer.rb. There are configuration options for the following:

the method that determines whether a user has permission to manage features (see admin permissions)
the method that returns the object that has features (e.g. User, Person, or Account; see feature recipients)
whitelists and blacklists for features (see white- and blacklisting)

CSS

Open up the newly-generated public/stylehseets/arturo_customizations.css. You can add any overrides you like to the feature configuration page styles here. Do not edit public/stylehseets/arturo.css as that file may be overwritten in future updates to Arturo.

In other frameworks

Arturo is a Rails engine. I want to promote reuse on other frameworks by extracting key pieces into mixins, though this isn't done yet. Open an issue and I'll be happy to work with you on support for your favorite framework.

Deep-Dive

Admin Permissions

Arturo::FeatureManagement#may_manage_features? is a method that is run in the context of a Controller or View instance. It should return true if and only if the current user may manage permissions. The default implementation is as follows:

current_user.present? && current_user.admin?

You can change the implementation in config/initializers/arturo_initializer.rb. A reasonable implementation might be

Arturo.permit_management do
  signed_in? && current_user.can?(:manage_features)
end

Feature Recipients

Clients of Arturo may want to deploy new features on a per-user, per-project, per-account, or other basis. For example, it is likely Twitter deployed "#newtwitter" on a per-user basis. Conversely, Facebook -- at least in its early days -- may have deployed features on a per-university basis. It wouldn't make much sense to deploy a feature to one user of a Basecamp project but not to others, so 37Signals would probably want a per-project or per-account basis.

Arturo::FeatureAvailability#feature_recipient is intended to support these many use cases. It is a method that returns the current "thing" (a user, account, project, university, ...) that is a member of the category that is the basis for deploying new features. It should return an Object that responds to #id.

The default implementation simply returns current_user. Like Arturo::FeatureManagement#may_manage_features?, this method can be configured in config/initializers/arturo_initializer.rb. If you want to deploy features on a per-account basis, a reasonable implementation might be

Arturo.feature_recipient do
  current_account
end

Arturo.feature_recipient do
  current_user.account
end

If the block returns nil, the feature will be disabled.

Whitelists & Blacklists

Whitelists and blacklists allow you to control exactly which users or accounts will have a feature. For example, if all premium users should have the :awesome feature, place the following in config/initializers/arturo_initializer.rb:

Arturo::Feature.whitelist(:awesome) do |user|
  user.account.premium?
end

If, on the other hand, no users on the free plan should have the :awesome feature, place the following in config/initializers/arturo_initializer.rb:

Arturo::Feature.blacklist(:awesome) do |user|
  user.account.free?
end

If you want to whitelist or blacklist large groups of features at once, you can move the feature argument into the block:

Arturo::Feature.whitelist do |feature, user|
  user.account.has?(feature.to_sym)
end

Feature Conditionals

All that configuration is just a waste of time if Arturo didn't modify the behavior of your application based on feature availability. There are a few ways to do so.

Controller Filters

If an action should only be available to those with a feature enabled, use a before filter. The following will raise a 403 Forbidden error for every action within BookHoldsController that is invoked by a user who does not have the :hold_book feature.

class BookHoldsController < ApplicationController
  require_feature :hold_book
end

require_feature accepts as a second argument a Hash that it passes on to before_filter, so you can use :only and :except to specify exactly which actions are filtered.

If you want to customize the page that is rendered on 403 Forbidden responses, put the view in RAILS_ROOT/app/views/arturo/features/forbidden.html.erb. Rails will check there before falling back on Arturo's forbidden page.

Conditional Evaluation

Both controllers and views have access to the if_feature_enabled and feature_enabled? methods. The former is used like so:

<% if_feature_enabled?(:reserve_table) %>
  <%= link_to 'Reserve a table', new_restaurant_reservation_path(:restaurant_id => @restaurant) %>
<% end %>

The latter can be used like so:

def widgets_for_sidebar
  widgets = []
  widgets << twitter_widget if feature_enabled?(:twitter_integration)
  ...
  widgets
end

Rack Middleware

require 'arturo'
use Arturo::Middleware, :feature => :my_feature

Outside a Controller

If you want to check availability outside of a controller or view (really outside of something that has Arturo::FeatureAvailability mixed in), you can ask either

Arturo.feature_enabled_for?(:foo, recipient)

or the slightly fancier

Arturo.foo_enabled_for?(recipient)

Both check whether the foo feature exists and is enabled for recipient.

Caching

Note: Arturo has support for caching Feature lookups, but doesn't yet integrate with Rails's caching. This means you should be very careful when caching actions or pages that involve feature detection as you will get strange behavior when a user who has access to a feature requests a page just after one who does not (and vice versa).

To enable caching Feature lookups, mix Arturo::FeatureCaching into Arturo::Feature and set the cache_ttl. This is best done in an initializer:

Arturo::Feature.extend(Arturo::FeatureCaching)
Arturo::Feature.cache_ttl = 10.minutes

You can also warm the cache on startup:

Arturo::Feature.warm_cache!

This will pre-fetch all Features and put them in the cache.

The following is the intended support for integration with view caching:

Both the require_feature before filter and the if_feature_enabled block evaluation automatically append a string based on the feature's last_modified timestamp to cache keys that Rails generates. Thus, you don't have to worry about expiring caches when you increase a feature's deployment percentage. See Arturo::CacheSupport for more information.

The Name

Arturo gets its name from Professor Maximillian Arturo on Sliders.